19-0411; Rev 4; 12/05
4-Pin µP Voltage Monitors
with Manual Reset Input
________________General Description
The MAX811/MAX812 are low-power microprocessor
(µP) supervisory circuits used to monitor power sup-
plies in µP and digital systems. They provide excellent
circuit reliability and low cost by eliminating external
components and adjustments when used with 5V-
powered or 3V-powered circuits. The MAX811/MAX812
also provide a debounced manual reset input.
These devices perform a single function: They assert a
reset signal whenever the V
CC
supply voltage falls
below a preset threshold, keeping it asserted for at
least 140ms after V
CC
has risen above the reset thresh-
old. The only difference between the two devices is that
the MAX811 has an active-low RESET output (which is
guaranteed to be in the correct state for V
CC
down to
1V), while the MAX812 has an active-high RESET out-
put. The reset comparator is designed to ignore fast
transients on V
CC
. Reset thresholds are available for
operation with a variety of supply voltages.
Low supply current makes the MAX811/MAX812 ideal
for use in portable equipment. The devices come in a
4-pin SOT143 package.
____________________________Features
♦
Precision Monitoring of 3V, 3.3V, and 5V
Power-Supply Voltages
♦
6µA Supply Current
♦
140ms Min Power-On Reset Pulse Width;
RESET
Output (MAX811), RESET Output (MAX812)
♦
Guaranteed Over Temperature
♦
Guaranteed
RESET
Valid to V
CC
= 1V (MAX811)
♦
Power-Supply Transient Immunity
♦
No External Components
♦
4-Pin SOT143 Package
MAX811/MAX812
_______________Ordering Information
PART*
MAX811_EUS-T
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
4 SOT143
________________________Applications
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
MAX812_EUS-T
-40°C to +85°C
4 SOT143
*This
part offers a choice of five different reset threshold volt-
ages. Select the letter corresponding to the desired nominal
reset threshold voltage, and insert it into the blank to complete
the part number.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
RESET THRESHOLD
SUFFIX
L
M
T
S
R
VOLTAGE (V)
4.63
4.38
3.08
2.93
2.63
___________Typical Operating Circuit
V
CC
V
CC
V
CC
___________________Pin Configuration
TOP VIEW
GND
1
4
V
CC
MAX811
MAX812
MR
GND
RESET
(RESET)
μP
RESET
INPUT
(RESET) RESET
GND
2
MAX811
MAX812
3
MR
SOT143
PUSHBUTTON
SWITCH
( ) ARE FOR MAX812
( ) ARE FOR MAX812
NOTE: SEE LAST PAGE FOR MARKING INFORMATION.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
4-Pin µP Voltage Monitors
with Manual Reset Input
MAX811/MAX812
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
V
CC
......................................................................-0.3V to 6.0V
All Other Inputs.......................................-0.3V to (V
CC
+ 0.3V)
Input Current, V
CC,
MR
.......................................................20mA
Output Current, RESET or
RESET
.......................................20mA
Continuous Power Dissipation (T
A
= +70°C)
SOT143 (derate 4mW/°C above +70°C) .......................320mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= 5V for L/M versions, V
CC
= 3.3V for T/S versions, V
CC
= 3V for R version, T
A
= -40°C to +85°C, unless otherwise noted.
Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Operating Voltage Range
Supply Current
SYMBOL
V
CC
I
CC
CONDITIONS
T
A
= 0°C to +70°C
T
A
= -40°C to +85°C
MAX81_L/M, V
CC
= 5.5V, I
OUT
= 0
MAX81_R/S/T, V
CC
= 3.6V, I
OUT
= 0
MAX81_L
MAX81_M
Reset Threshold
V
TH
MAX81_T
MAX81_S
MAX81_R
Reset Threshold Tempco
V
CC
to Reset Delay (Note 2)
Reset Active Timeout Period
MR
Minimum Pulse Width
MR
Glitch Immunity (Note 3)
MR
to Reset Propagation Delay
(Note 2)
t
MD
V
IH
MR
Input Threshold
V
IL
V
IH
V
IL
MR
Pull-Up Resistance
V
OH
RESET Output Voltage
(MAX812)
I
SOURCE
= 150µA, 1.8V < V
CC
< V
TH(MIN)
MAX812R/S/T only, I
SINK
= 1.2mA,
V
CC
= V
TH(MAX)
MAX812L/M only, I
SINK
= 3.2mA,
V
CC
= V
TH(MAX)
V
CC
> V
TH(MAX)
, MAX81_L/M
V
CC
> V
TH(MAX)
, MAX81_R/S/T
2.3
0.8
0.7 x V
CC
0.25 x V
CC
10
0.8 x V
CC
0.3
0.4
V
20
30
kΩ
V
t
RP
t
MR
V
OD
= 125mV, MAX81_L/M
V
OD
= 125mV, MAX81_R/S/T
V
CC
= V
TH(MAX)
140
10
100
0.5
T
A
= +25°C
T
A
= -40°C to +85°C
T
A
= +25°C
T
A
= -40°C to +85°C
T
A
= +25°C
T
A
= -40°C to +85°C
T
A
= +25°C
T
A
= -40°C to +85°C
T
A
= +25°C
T
A
= -40°C to +85°C
4.54
4.50
4.30
4.25
3.03
3.00
2.88
2.85
2.58
2.55
30
40
20
560
2.63
2.93
3.08
4.38
MIN
1.0
1.2
6
2.7
4.63
15
10
4.72
4.75
4.46
4.50
3.14
3.15
2.98
3.00
2.68
2.70
ppm/°C
µs
ms
µs
ns
µs
V
TYP
MAX
5.5
UNITS
V
µA
V
OL
2
_______________________________________________________________________________________
4-Pin µP Voltage Monitors
with Manual Reset Input
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 5V for L/M versions, V
CC
= 3.3V for T/S versions, V
CC
= 3V for R version, T
A
= -40°C to +85°C, unless otherwise noted.
Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MAX811R/S/T only, I
SINK
= 1.2mA,
V
CC
= V
TH(MIN)
V
OL
RESET
Output Voltage
(MAX811)
V
OH
MAX811L/M only, I
SINK
= 3.2mA,
V
CC
= V
TH(MIN)
I
SINK
= 50µA, V
CC
> 1.0V
MAX811R/S/T only, I
SOURCE
= 500µA,
V
CC
> V
TH(MAX)
MAX811L/M only, I
SOURCE
= 800µA,
V
CC
> V
TH(MAX)
0.8 x V
CC
V
CC
- 1.5
MIN
TYP
MAX
0.3
0.4
0.3
V
UNITS
MAX811/MAX812
Note 1:
Production testing done at T
A
= +25°C, over temperature limits guaranteed by design using six sigma design limits.
Note 2:
RESET
output for MAX811, RESET output for MAX812.
Note 3:
“Glitches” of 100ns or less typically will not generate a reset pulse.
_______________________________________________________________________________________
3
4-Pin µP Voltage Monitors
with Manual Reset Input
MAX811/MAX812
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
(MAX81_R/S/T)
MAX811/12-TOC1
SUPPLY CURRENT vs. TEMPERATURE
(MAX81_L/M)
MAX811/12-TOC2
POWER-DOWN RESET DELAY vs. TEMPERATURE
(MAX81_R/S/T)
V
OD
= V
TH
- V
CC
V
OD
= 20mV
MAX811/12-TOC3
3.0
2.5
SUPPLY CURRENT (μA)
2.0
1.5
1.0
0.5
0
-40
-15
10
35
60
V
CC
= 3.6V
V
CC
= 3.3V
8
100
POWER-DOWN RESET DELAY (μs)
SUPPLY CURRENT (μA)
6
V
CC
= 5.5V
80
60
4
40
V
OD
= 125mV
20
V
OD
= 200mV
0
2
V
CC
= 1V
0
85
-40
-15
TEMPERATURE (°C)
V
CC
= 3V
V
CC
= 1V
10
35
TEMPERATURE (°C)
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
POWER-DOWN RESET DELAY vs. TEMPERATURE
(MAX81_L/M)
MAX811/12-TOC4
POWER-UP RESET TIMEOUT
vs. TEMPERATURE
MAX81_R/S/T
POWER-UP RESET TIMEOUT (ms)
220
MAX811/12-TOC5
RESET THRESHOLD DEVIATION
vs. TEMPERATURE
MAX811/12-TOC6
200
POWER-DOWN RESET DELAY (μs)
V
OD
= V
TH
- V
CC
V
OD
= 20mV
230
1.0005
1.0000
150
NORMALIZED THRESHOLD (V)
0.9995
100
210
0.9990
50
V
OD
= 125mV
V
OD
= 200mV
-40
-15
10
35
60
85
TEMPERATURE (°C)
200
MAX81_L/M
0.9985
0.9980
0
190
-40
-15
10
35
60
85
TEMPERATURE (°C)
-40
-15
10
35
60
85
TEMPERATURE (°C)
4
_______________________________________________________________________________________
4-Pin µP Voltage Monitors
with Manual Reset Input
______________________________________________________________ Pin Description
PIN
NAME
MAX811
1
2
MAX812
1
—
GND
RESET
Ground
Active-Low Reset Output.
RESET
remains low while V
CC
is below the reset threshold or while
MR
is held low.
RESET
remains low for the Reset Active Timeout Period (t
RP
) after the reset
conditions are terminated.
Active-High Reset Output. RESET remains high while V
CC
is below the reset threshold or while
MR
is held low. RESET remains high for Reset Active Timeout Period (t
RP
) after the reset condi-
tions are terminated.
Manual Reset Input. A logic low on
MR
asserts reset. Reset remains asserted as long as
MR
is
low and for 180ms after
MR
returns high. This active-low input has an internal 20kΩ pull-up
resistor. It can be driven from a TTL or CMOS-logic line, or shorted to ground with a switch.
Leave open if unused.
+5V, +3.3V, or +3V Supply Voltage
FUNCTION
MAX811/MAX812
—
2
RESET
3
3
MR
4
4
V
CC
_______________ Detailed Description
Reset Output
A microprocessor’s (µP’s) reset input starts the µP in a
known state. These µP supervisory circuits assert reset
to prevent code execution errors during power-up,
power-down, or brownout conditions.
RESET
is guaranteed to be a logic low for V
CC
> 1V.
Once V
CC
exceeds the reset threshold, an internal
timer keeps
RESET
low for the reset timeout period;
after this interval,
RESET
goes high.
If a brownout condition occurs (V
CC
dips below the
reset threshold),
RESET
goes low. Any time V
CC
goes
below the reset threshold, the internal timer resets to
zero, and
RESET
goes low. The internal timer starts
after V
CC
returns above the reset threshold, and
RESET
remains low for the reset timeout period.
The manual reset input (MR) can also initiate a reset.
See the
Manual Reset Input
section.
The MAX812 has an active-high RESET output that is
the inverse of the MAX811’s
RESET
output.
Manual Reset Input
Many µP-based products require manual reset capabil-
ity, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. A logic low on
MR
asserts reset. Reset remains asserted while
MR
is low,
and for the Reset Active Timeout Period (t
RP
) after
MR
returns high. This input has an internal 20kΩ pull-up
resistor, so it can be left open if it is not used.
MR
can
be driven with TTL or CMOS-logic levels, or with open-
drain/collector outputs. Connect a normally open
momentary switch from
MR
to GND to create a manual-
reset function; external debounce circuitry is not
required. If
MR
is driven from long cables or if the
device is used in a noisy environment, connecting a
0.1µF capacitor from
MR
to ground provides additional
noise immunity.
Reset Threshold Accuracy
The MAX811/MAX812 are ideal for systems using a 5V
±5% or 3V ±5% power supply with ICs specified for 5V
±10% or 3V ±10%, respectively. They are designed to
meet worst-case specifications over temperature. The
reset is guaranteed to assert after the power supply
falls out of regulation, but before power drops below
the minimum specified operating voltage range for the
system ICs. The thresholds are pre-trimmed and exhibit
tight distribution, reducing the range over which an
undesirable reset may occur.
_______________________________________________________________________________________
5
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